Security seals are known of the type comprising a length of wire which has been so made that when a seal is made by twisting at least one end around the other end an attempt to untwist said at least one end is substantially likely to result in fracture of the wire.
In some instances the wire is of such character or has been treated to have such character as to so substantially work harden as to fracture if that untwisting should be performed. In an alternative but which may be additional to the previous the wire is provided with lines of preferential fracture on the part thereof which will be an inside curve after the twisting and at which lines the wire will tend to fracture if that untwisting should be performed. Those lines of preferential fracture may be produced by stamping the wire and this may be done to produce substantial work hardening thereof and/or reduced cross-section in localities.
Unfortunately, criminals have discovered that security seals of the above type can often be successfully tampered with without leading to such fracture if the wire is heated in the region in which it has been twisted prior to untwisting. Indeed, if sufficient heat is applied the wire can be re-twisted after untwisting to give the appearance that the wire has not been tampered with.
Since distant visual sighting of such seals is an important aspect of maintaining security of railway wagons, containers and trucks, this new found ability to tamper without this being remotely discernable is most inconvenient to those wishing to maintain security of goods and establishments.